You can connect as many domains to your main domain as you want by using the Redirect Domain Tool.
To redirect another domain to your website:
Go to your website Dashboard.
Click the Domain button and select Set unique domain from the list.
Click the Add Existing Domain button and enter the domain you want to redirect to your main domain.
Click the Domain button again, and select Redirect Domains from the list.
Click the Redirect a new domain button.
Enter the domain (including www) and Save.
The domain you wish to redirect to your main domain must point to SITE123 using the following records:
A Record that points to 188.8.131.52
CNAME for www that points to ssl.site123.com